Gas turbine engine noise shield

ABSTRACT

Positionable deflector means are provided in a gas turbine engine inlet duct. The deflector means are actuated to change the axial and circumferential location of a forward protruding extension of the inlet duct in order to selectively reduce noise propagation. A method is disclosed for directional noise shielding as a gas turbine engine experiences altitude and operational changes.

This is a division of application Ser. No. 503,750, filed Sept. 6, 1974.

BACKGROUND OF THE INVENTION

In the present era of environmental awareness, the gas turbine enginedesigner, and particularly the designer of such engines for aircraftpropulsion, is faced with the dilemma of reducing engine pollutants witha minimum sacrifice of engine performance. One type of pollution whichrecently has received considerable attention is noise.

Gas turbine engine noise is generated from two primary sources: first,there is that associated with the viscous shearing of rapidly movinggases exhausted into the relatively quiescent surrounding atmosphere. Inturbofan aircraft engines, such gases are emitted from the fan and corenozzles at the rear of the engine. Various approaches have been utilizedto reduce this "shear" noise, most approaches incorporating mixers tocomingle fan and exhaust gases with each other and with the surroundingenvironment.

The second source of noise, and the one to which the present inventionis directed, is generated by the rotating turbomachinery itself, theresult of rapidly rotating blade rows disposed within the gas stream.The noise is affected by such parameters as blade rotational speed,blade-to-blade spacing, blade geometry and also by the proximity ofstationary hardware to such rotating blade rows, as in the case of anoutlet guide vane arrangement and in typical multistage axialcompressors where stationary blade rows are alternated with rotatingblade rows. Some of the noise generated in this manner can be absorbedand suppressed by means of acoustic or sound absorbing paneling disposedabout the periphery of the nacelle enclosing the rotatingturbomachinery. Such sound-absorbing material is well known in the art.However, a significant percentage of noise propagates forward from thegas turbine inlet duct due to the proximity of the fan or compressor tothe inlet frontal plane and the lack of forward shielding in the forwarddirection. The problem, therefore, facing the gas turbine designer is toprovide a means for attenuating this forward propagating noise withoutincurring overall performance penalties.

Prior state of the art concepts to attempt to solve this problem haveconcentrated on the addition of sound-absorbing material upon the inletduct inner wall. This does little to attenuate unreflected noisepropagating in the axially forward direction. Additional benefits havebeen obtained by providing coaxial, circumferential rings of soundabsorbent material within the inlet. However, such rings produce a lossof inlet total pressure and, therefore, performance losses which remainthroughout the engine operating envelope even where noise propagationpresents no hazard or nuisance to inhabitants below.

Another concept incorporates an axially translating scoop on the bottomof the inlet duct to selectively reduce the downward transmission ofnoise from the inlet. However, this concept does little to protectagainst the nuisance of noise in one of the most critical engineoperating regimes; that is, when the engine is at ground altitude.Downward propagating noise in this environment is shielded by the grounditself, while side propagating noise remains unattenuated.

SUMMARY OF THE INVENTION

Accordingly, it is the primary object of this invention to selectivelyreduce aerodynamically induced noise propagating from the inlet of a gasturbine engine without sacrificing overall engine performance.

This and other objects and advantages will be more clearly understoodfrom the following detailed decription, the drawings and specificexamples, all of which are intended to be typical of rather than in anyway limiting the present invention.

Briefly stated, the above object is attained by providing a movablenoise deflector about the inlet duct and scheduling, through anactuating means, the change in axial and circumferential position of thedeflector in relation to the engine operating environment. As thealtitude and operating environment of the engine change, the deflectorcan be programmed to shield the noise in those directions deemed mostobjectionable. In an alternative embodiment, a plurality of deflectormembers is provided about the periphery of the inlet duct, these membersbeing axially translatable with respect to the fixed inlet duct.Predetermined of these members may be translated forward of the fixedinlet frontal plane, again providing directional noise shielding. Whilethis invention will aid in inlet noise suppression, most significant isthat it will accomplish this suppression without overall engineperformance penalties since there is no encroachment into the stream ofair entering the engine.

DESCRIPTION OF THE DRAWINGS

While the specification concludes with a series of claims particularlypointing out and distinctly claiming the subject matter which isregarded as part of the present invention, it is believed that theinvention will be more fully understood from the following descriptionof the preferred embodiments which are given in connection with theaccompanying drawings, in which:

FIG. 1 is a schematic representation of a gas turbine engineincorporating the subject invention;

FIG. 2 is an enlarged, isometric view of the gas turbine engine inlet ofFIG. 1 incorporating the present invention;

FIG. 3 is a schematic representation of the utilization of the presentinvention to suppress/deflect noise in a predetermined circumferentialdirection;

FIG. 4 is similar to FIG. 3 and represents the present invention beingutilized in an alternative embodiment;

FIG. 5 is a schematic representation of the utilization of the presentinvention to deflect noise in the axial direction; and

FIG. 6 is similar to FIG. 2 and represents an alternative embodiment ofthe subject invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings wherein like numerals correspond to likeelements throughout, reference is initially directed to FIG. 1 whereinan engine depicted generally at 10 embodying the present invention isdiagrammatically shown. This engine may be considered as comprisinggenerally a core engine 11, a fan assembly 12, and a fan turbine 14which is interconnected to the fan assembly 12 by shaft 16. The coreengine 11 includes an axial flow compressor 18 having a rotor 20. Airenters inlet assembly 22 and is initially compressed by fan assembly 12.A first portion of this compressed air enters the fan bypass duct 24 andsubsequently discharges through a fan nozzle 25. A second portion of thecompressed air enters inlet 26, is further compressed by the axial flowcompressor 18 and then is dicharged to a combustor 28 where fuel isburned to provide high energy combustion gases which drive a turbine 30.The turbine 30, in turn, drives the rotor 20 through a shaft 32 in theusual manner of a gas turbine engine. The hot gases of combustion thenpass to and drive the fan turbine 14 which, in turn, drives the fanassembly 12. The propulsive force is thus obtained by the action of thefan assembly 12, discharging air from the fan bypass duct 24 through thefan nozzle 34 and by the discharge of combustion gases from a coreengine nozzle 36 defined, in part, by plug 38.

The above description is typical of many present-day engines and is notmeant to be limiting, as it will become readily apparent from thefollowing description that the present invention is capable ofapplication to any gas turbine engine with or without a fan and may beused to selectively shield noise propagating from any type of duct. Theabove description of the engine depicted in FIG. 1 is therefore merelymeant to be illustrative of one type of application.

Referring now to FIG. 2, the inlet assembly 22 of FIG. 1 is shown toinclude a fixed cylindrical duct 40, a lip 42 defining an inlet frontalplane 44 and a movable, arcuate deflector member 46 essentially coaxialwith the fixed duct longitudinal axis. The deflector member 46 isoperatively connected by one of a variety of state of the art actuators47 (FIG. 1) to the fixed inlet duct. Such an actuator is capable oftranslating the deflector 46 from a stowed position essentially flushwith the inlet frontal plane 44 to an extended position designated A--Aahead of the inlet frontal plane. It would further be capable ofrotating the deflector 46 from a first predetermined circumferentialposition A--A to a second predetermined circumferential position B--B.

Typically, noise produced by a gas turbine engine is transmitted equallyin all directions forward of the inlet frontal plane 44. Since gasturbine engines find their predominant application in aircraftpropulsion, as the aircraft changes altitude and orientation the noisecreating a nuisance to fixed targets (such as towns, persons, homes,etc.) is that radiating from different inlet circumferential locations.For example, FIG. 3 depicts a gas turbine engine 10 installed on anaircraft wherein the aircraft is in a relatively low altitude operatingcondition, such as take-off or landing. In such an orientation, theobjectionable noise is that transmitted in the essentially downwarddirection within circumferential sector 48. However, during groundoperations, objectionable noise is typically that radiating from theside of the engine inlet (sector 50, FIG. 4) since the ground itselfserves as a deflector of sound in the downward direction (and rarely isthere a target requiring protection in that location while an aircraftis on the ground).

The present invention provides a means of selectively shielding noise inpredetermined directions to provide continual protection as the gasturbine engine and aircraft change operating orientation. In thepreferred embodiment of FIG. 2, the arcuate deflector member 46 ispositionable about the circumference of the inlet lip 42 and is alsoaxially translatable with respect to the fixed inlet 22. As depicted inFIG. 5, with the deflector member 46 extended from the inlet frontalplane to position A, sound suppression is provided in an areaessentially within the included angle θ constructed between the inletfrontal plane 44 and the line 52, wherein line 52 is drawn from a point54 on the inlet lip opposite the deflector member 46 tangent to theforward-most extension of the deflector member 46. As the deflectormember is withdrawn to positionA', only the area within included angleθ' (between plane 44 and line 52') receives the benefit of soundsuppression. Therefore, by varying the axial extension of the deflectormember 46 selective shielding in the essentially axial direction may beobtained. At predetermined altitudes, above which gas turbine enginenoise is no longer objectionable to inhabitants below, the deflectormember 46 can be withdrawn flush with the inlet frontal plane.Additionally, by rotating the deflector member 46 about thecircumference of the inlet the zone of protection may be altered as, forexample, from sector 48 to sector 50 of FIGS. 3 and 4, respectively.Suppression may be further enhanced by providing sound absorbingmaterial 56 upon the radially inward surface of the deflector member 46.

An alternative embodiment of the subject invention appears in FIG. 6.Therein, a plurality of movable, arcuate deflector members 46 aredisposed about the circumference of the inlet duct 22, each axiallytranslatable with respect to the inlet duct and capable of extensionforward of the fixed inlet frontal plane 44. Directional sounddeflection is attained through selective axial positioning of apredetermined number of deflector members 46. Again, one of a variety ofstate of the art actuating means is adaptable to this purpose. As isreadily apparent, the results of selective sound suppression of thealternative embodiment of FIG. 6 are similar to the results obtained inthe embodiment of FIG. 2. Significantly, in neither embodiment is itcontemplated that any structure extend into the inlet frontal plane 44to disrupt the flow of air. Therefore, no reduction of inlet totalpressure will be produced resulting in overall performance degradation.

It should be obvious to one skilled in the art that certain changes canbe made to the above-described invention without departing from thebroad inventive concepts thereof. For example, a plurality of axiallyand circumferentially movable deflector members could be employed in theembodiment of FIG. 2 to provide simultaneous protection in multiplecircumferential sectors. Also, the inlet need not be cylindrical and thedeflector members need not be arcuate. Additionally, this inventioncontemplates the utilization of the deflector members to inhibit theingestion of foreign objects into the inlet when the engine is operatingin a near ground level environment, either in conjunction with soundsuppression, or singly when sound suppression is of no importance. It isintended that the appended claims cover these and all similar variationsin the present invention's broader inventive concept.

What I claim is:
 1. A turbofan engine comprising:a core engineincluding, in series flow relationship, an axial flow compressor, acombustor to which pressurized air from the compressor and fuel aredelivered for combustion therein to provide a hot gas stream, a firstturbine downstream of said combustor adapted to be rotatably driven bysaid hot gas stream, and a shaft drivingly connecting said compressorrotor and said first turbine; a second turbine rotatable independentlyof the rotatable elements of the core engine, said second turbinedisposed downstream of said first turbine and adapted to be rotatablydriven by said hot gas stream; an inlet assembly for selectivelyreducing noise propagation, said inlet assembly comprising an inletduct, said duct disposed about at least a portion of said core engine;and a fan assembly disposed in said duct for pressurizing air flowthrough said duct, said fan drivingly connected to said second turbine;said inlet assembly further comprising movable deflector means, saiddeflector means operatively connected to an actuating means whereby saiddeflector means is axially positionable at a first effective operatingposition within a first sector of said inlet duct, and further axiallypositionable at at least a second effective operating position within asecond sector of said inlet duct, wherein said second sector iscircumferentially disposed from said first sector.